Analysis of bio-anode performance through electrochemical impedance spectroscopy

•Impedance spectra were translated to charge and diffusion resistances.•Rt decreased 100–1000 × upon increasing buffer to 100 mM and acetate to 20 mM.•Lowest values were 144 Ω·cm2 for Rct and 34 Ω·cm2 for Rd.•Relationship between saturation current and inverse Rct was linear.

In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm− 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture.In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm− 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 Ω·cm2 and 34 Ω·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration.